The field of the invention is that of internal combustion engines and the invention relates more particularly to internal combustion engines having a fuel heater for enhancing fuel vaporization before the fuel is furnished to engine cylinders.
Conventional internal combustion engines combine air and fuel in selected ratios for furnishing to engine cylinders and typically arrange electrical resistance heater elements to heat the fuel to enhance fuel vaporization to assure or maintain a desired air-fuel ratio, particularly during engine warm-up on a cold day. In one widely used engine system for example, a self-regulating multi-passaged electrical resistance heater elemcnt of positive temperature coefficient of resistivity (PTC) is disposed between a carburetor and an intake manifold so that an air-fuel mixture substantially formed in the carburetor is passed through the heater element to be fully vaporized to complete formation of the air-fuel mixture before it is advanced to the engine cylinders. In another widely used engine system a heater plate is mounted in an opening in the bottom of an intake manifold beneath a carburetor for intercepting and heating air and fuel directed into the intake manifold before the manifold distributes the air-fuel mixture to individual engine cylinders. In other more recently proposed engine systems of the fuel injector type, fuel injectors are arranged to direct fuel into inlet channels in a cylinder head to provide precisely regulated air-fuel ratios to individual engine cylinders and electrical resistance heater elements are disposed in the respective cylinder head channels to intercept and heat fuel sprayed from the individual injectors to achieve the desired air-fuel ratio even during engine start-up on a cold day. However, it would be desirable in some of those engine systems such as those for four cylinder engines if fewer heater elements could be used in providing adequate fuel heating, if such fuel heating could be achieved with less interference with the flow of an air-fuel mixture to the engine cylinders or with less interference with distribution of the air-fuel mixture to the different cylinders, if such heater elements could be accommodated in otherwise conventional engines with less interference with coolant fluid passages and the like, and if heating of the fuel could be achieved closer to furnishing of the air-fuel mixture to the cylinders particularly in the case of engine systems having two intake valves for each cylinder.